Frank J. Wilstach, comp. A Dictionary of Similes. 1916.
Sincere
Sincere as sunlight.
—Anonymous
As truth, sincere.
—David Mallet
About as sincere as the look upon the face of an undertaker conducting a nine-hundred dollar funeral.
—Henry L. Mencken
Sincerity is like travelling on a plain, beaten road, which commonly brings a man sooner to his journey’s end than byways, in which men often lose themselves.
—John Tillotson